The embodiments described herein relate generally to apparatus and methods for insertion of a cannula into target tissue, and more particularly, to cutting target tissue and inserting a cannula of a ventricular assist device into the left atrium of a heart.
The use of devices to assist the function of an ailing heart is increasing. In some instances, a ventricular assist device (VAD) can be used to partially or completely replace the function of the heart. For example, in some instances, a left ventricular assist device (LVAD) can be used to assist a heart of a patient by placing an inlet flow cannula in fluid communication with the left atrium of the heart and an outlet flow cannula in fluid communication with a portion of the aorta. The LVAD can include a pumping mechanism that can pump, transfer, draw, push, or otherwise produce a flow of blood between the inlet flow cannula and the outlet flow cannula, thereby assisting heart.
Some known methods for placing an inlet flow cannula in or at a desired location within, for example, the left atrium include advancing the inlet flow cannula through the superior vena cava (SVC) and piercing the septum between the right atrium and the left atrium. In such methods, the thickness of the septum can be sufficient to allow piercing and/or cutting thereof to provide the passage of the inlet flow cannula. Such methods, however, often include an at least partially blind piercing of the septum, which can be challenging and can result in undesirable placement of the inlet flow cannula. Some such methods can be used with imaging techniques such as, fluoroscopy and echocardiography, however, due to the distance between the insertion point and the target location of the heart and/or the torturous path of the anatomy, precision can still be difficult and the ability to apply a suitable force can be challenging.
In other instances, methods for placing an inlet flow cannula in or at a desired location within the left atrium include coupling the inlet flow cannula to the dome of the left atrium. This location can provide performance benefits because it is adjacent a wider portion of the left atrium and is remote from the left and right pulmonary veins. Coupling of the inlet flow cannula to the dome of the left atrium, however, can be complicated by the anatomy of the heart. For example, the walls of the dome of the left atrium are very thin (e.g., between 1 and 2 mm in thickness) and fragile, which can make incising the tissue difficult. Moreover, certain procedures may include dilating an incision in the atrial wall with a dilator and/or balloon catheter, for example, to accommodate the desired size of the inlet flow cannula. Dilation of certain tissue, such as the dome of the atrium can lead to tearing of the tissue and/or fracture that can extend beyond a diameter of the dilator (e.g., due at least in part on the thinness of the tissue). In addition, the interior of the atrium can be at a relatively low pressure, due to the function of the heart. Therefore, when the dome of the left atrium is pushed and/or manipulated from the outside to incise or dilate the tissue (e.g., with a scalpel or other tool), the tissue can collapse into the atrium, making a clean cut of the atrium wall difficult to achieve. In some instances, similar collapse can occur in, for example, transseptal puncture and/or a puncture through the right atrial wall.
Thus, a need exists for improved apparatus and methods for cutting target tissue and inserting a cannula of a ventricular assist device into the left atrium of a heart.